There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like, while lowering the costs of manufacturing such devices. This drive is, in part, fueled by consumer demands for faster, higher quality computers and electronic devices at lower prices. These demands have resulted in continual improvements in the manufacturing of semiconductor devices.
In manufacturing semiconductor devices, it is a well-known practice to use feedback controllers to ensure high quality and low cost. An example of a feedback controller system 100, shown in FIG. 1, includes a tool 103 and a feedback controller 107 coupled each other. The tool 103 can be one or any combination of semiconductor-manufacturing tools such as a chemical mechanical planarization (CMP) tool, a depositor, an etcher, etc. In particular, the tool 103 receives wafers as input 101 and processes them according to a set of control parameters 109, e.g., recipes received from the controller 107. The processed wafers are referred to as outputs 105. Examples of processes are depositing a new layer of film, etching a layer, etc.
Once the tool 103 processes a wafer, one or more metrology stations, not shown in FIG. 1, make measurements on the processed wafer. The measurements are communicated to the controller 107. The controller 107 then compares the measurements to predicted values calculated previously. Based on the comparison, the controller 107 makes adjustments to the control parameters 109. For example, if the thickness of a newly deposited layer is outside of a desired range when the measurement is compared with the predicted value, the controller 107 adjusts one or more of the control parameters 109, e.g., the amount of gas flow, the length of processing time, etc., to deposit a thinner film on the next wafer. The tool 103 then receives another wafer and processes the wafer using the adjusted control parameters.
The performance of the feedback controller depends on, in part, receiving accurate measurements from the metrology stations. When inaccurate or erroneous measurements are received, the feedback controller needs to identify such measurements and have a mechanism to prevent such measurements from affecting the operation. In conventional feedback controllers, no robust mechanism was provided to address erroneous measurements. When erroneous measurements are entered repeatedly to the controller 107, they cause increased defects, low yields, or both in devices formed on processed wafers.